1. Field of the Invention
The present invention relates to an apparatus for driving an ink jet head, which ejects an ink droplet from a nozzle by changing the capacity of a pressure chamber for containing an ink therein.
2. Description of the Related Art
For example, in Jpn. Pat. Appln. KOKAI Publication No. 2000-43251, there is described a driving method for carrying out gradation printing by using an ink jet recording apparatus which ejects an ink from a nozzle by changing the capacity of an ink chamber to be expanded or contracted, the ink chamber containing an ink, by using a piezoelectric element.
In this publication, the following description is given. Namely, conventionally, when large-liquid-droplet driving, middle-liquid-droplet driving, and small-liquid-droplet driving are carried out for the purpose of gradation printing, there has been a problem that times for terminating these driving operations vary from one another, and the residual vibration energies also vary from one another. Inevitably, the residual vibration of the ink impose different influences on the ink chambers as the ink chambers are sequentially driven. This results in printing of poor quality. Thus, after a wait time has elapsed according to an ejection liquid quantity from a drive timing when starting a printing operation, the ink chambers are expanded. After a predetermined time interval has elapsed from the drive timing irrespective of the ejection liquid quantity, each of group of ink chambers is controlled so as to contract all the ink chambers. In this manner, the effect of the residual vibration on the ink chambers driven immediately after such control is substantially uniformed irrespective of an ink droplet ejection quantity of the ink chambers driven immediately before such control, thereby enabling stable printing control irrespective of the content of an image signal.
However, in the driving method of this publication, in the case where an ink ejection timing changes due to variety in relative velocity between an ink jet head and a recording medium, or the like, the velocity or volume of ejection ink droplets changes due to the effect of the residual vibration. As a result, there has been a problem with a lowered printing quality such as displacement of ink landing positions or occurrence of variety in printing dot size. In addition, during an ink ejecting operation, unwanted meniscus vibration due to the residual vibration generated immediately preceding ink ejecting operation is added. Therefore, there has been a problem that such an ink ejection operation itself is made unstable.